1. Field of Invention
The present invention relates to planar inverted-F antennas (PIFAs) and more particularly to such a PIFA with improved characteristics.
2. Description of Related Art
Our daily life becomes much convenient as technology (particularly mobile communication technology) has known a rapid, spectacular development in recent several decades. For example, mobile phones are widely used. As to mobile phones, one trend is to develop more compact mobile phones. In this regard, an antenna of a mobile phone is typically formed as an internal, miniature one.
As to antenna mounted in a mobile communication device (e.g., PDA (Personal Digital Assistant), mobile phone, or the like), the antenna is typically implemented as a PIFA. For example, U.S. Pat. No. 6,727,854 B2 discloses a PIFA for mobile phone as shown in FIG. 1. The PIFA comprises a radiating device. Three current paths 10, 14, and 15 are formed in the radiating device and each starts at a feed point 17 and terminates at a ground point 16. A resonance is generated due to the multiple current paths. As a result, the PIFA is adapted to operate in two or more frequencies. U.S. Patent Publication No. 2003/0103010 A1 discloses a dual-band antenna arrangement for a mobile phone handset as shown in FIG. 2. In a patch conductor, two current paths 20 and 24 formed in the patch conductor and each starts at a feed pin 25 and terminates at a shorting pin 26. A resonance is generated due to the multiple current paths. As a result, the antenna is adapted to operate in two or more frequencies.
Multiple current paths are the characteristic of both prior art antenna arrangements. The multiple current paths are adapted to control an operating frequency of the antenna. Further, it is required to adjust a resonance frequency by changing size of a radiating member. It is understood that a resonance frequency of an antenna is partly affected by the environment. This is particularly true for an internal antenna such as one mounted in a mobile phone. As such, time spent on finalizing the specifications of an antenna is relatively long. This inevitably prolongs the development time of a mobile communication product (e.g., mobile phone). This is a disadvantage since more and more new types and models of mobile phone are available in an even faster pace. That is, the market is very competitive and product life is shortened greatly. Thus, the need for improvement still exists in order to overcome the inadequacies of the prior art.